1. Field of the Invention:
This invention relates generally to an improvement in wear and seizing resistance of a sliding surface of a sliding member such as a piston used in an engine, on which a composite plating film is formed.
2. Description of the Prior Art:
Plated sliding surfaces of sliding members on which composite plating films are formed are known, such as:
(1) Gazette No. 55-154600 for Published Unexamined Patent Application (Published in Japan in 1980), and
(2) Gazette No. 57-71812 for Published Unexamined Patent Application (Published in Japan in 1982).
Publication (1) describes a nickel-plated sliding surface. In this technique, a composite nickel plating containing a solid lubricant is formed on a base surface with a micro three-dimensional structure so as to provide a composite nickel plating film with a three-dimensional structure on the base surface. Publication (2) describes a composite nickel plating method which uses extremely pure silicon carbide fine powder having an excellent dispersibility. In addition to these techniques, a hardening method using a nickel-phosphorus plating film is known. In this method, a nickel plating film having a phosphorus concentration of 5 to 12% is formed on a product. Then, it is heated to a temperature within a range of 270 to 400.degree. C. in a heating furnace and is kept at this temperature for 0.5 to 4 hours.
However, there are some drawbacks with these prior art techniques. In the process of publication (1) for forming the nickel-plated sliding surface on which a composite nickel plating film is formed, boron nitride as a solid lubricant is dispersed as a composite material in the nickel plating film so as to improve lubricating characteristics of the sliding surface. However, this sliding surface has poor wear and seizing resistance. In the process of publication (2) for forming the composite nickel plating film using a silicon carbide fine powder, silicon carbide fine particles having an average particle size of 1.mu. or less and dispersed in a nickel bath serve to improve wear resistance. However, the lubricating characteristics of the sliding surface are poor. In addition, silicon carbide particles separated from the sliding surface act as a abrasive which causes wear in a mating member.
In the method of hardening a nickel plating film having a phosphorus concentration of 5 to 12%, if the sliding member consists of Al or an Al alloy, a heat treatment for hardening the film results in degradation in the strength of the film material and a change in size of the member.